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Receiving Data of More than 1024 Bytes from Communication Partner Using CP-340 Module

Created by: Aevat at: 5/15/2012 7:42 AM (17 Replies)

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5/15/2012 7:42 AM	Rate (0)
Aevat Posts: 17 Rating: (0)	Hi, I'm reading data from a digital tester on CP-340 module using RS-232 (ASCII protocol). I can be able to fetch data by using the FB2 function (P_RECV). But the error occurs when the data that has to be received exceeded the 1024 bytes limit of the FB2. The error status code generated is "080A". I want to know now how to receive a data of more than 1024 bytes on CP-340 module. Thanks in advance!
Aevat Posts: 17 Rating: (0)
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5/15/2012 1:29 PM	Rate (3)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	I would seem that the CP340 only has enough buffer space for 1024 bytes. So you must read the data quickly enough such that this buffer space is never exceeded. Data off the wire will enters the buffer at one end. The P_RCV call removes the data from the other end of the buffer and transfers it to a DB within the PLC, thus creating more buffer space for incoming data off the wire. The process of pulling the data out of the buffer via the P_RCV call must be quicker than the speed at which the data is entering the buffer from the wire, else you will suffer a buffer overflow and get the 080A error. This is not usually a problem as the data enterring the buffer does so quite slowly in comparison to the speed of the PLC, provided you call the P_RCV call quickly enough. For example, at 9600 baud, the data is entering at 9600 bits per second (this is actually only an approximate value, but close enough for our purposes). If you are using (say) 8 data bits, 1 stop bit and no parity, this equates to 10 bits per byte (1 start bit + 8 data bits + 1 stop bit). So this equates to 960 bytes per second. So as long as you call the P_RCV call quicker than once per second, you should be fine. What OB are you using the P_RCV call in?
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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5/15/2012 1:58 PM	Rate (0)
Aevat Posts: 17 Rating: (0)	Thank you so much for your reply. As of now, I'm calling the FB2 function on OB1. As far as I can understand regarding your explanation, I can be able to retrieve data more than 1024 bytes without error if I call FB2, say twice in a second? In the current program I'm using, where I use a static signal 1 on the EN_R of FB2, I'm receiving only the excess data of the actual length of the data I wanted to receive. For example, the actual data that I need to fetch is 1034 bytes. When I start requesting for the data, the last 10 bytes only (bytes 1025-1034) are written on the DB I specified on FB2. How can I program this such that I can be able to receive all the 1034 bytes?... Thanks again in advance.
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5/15/2012 2:20 PM	Rate (0)
manmeet Gold Member Joined: 1/3/2006 Last visit: 2/19/2024 Posts: 726 Rating: (71)	Hi The Status code of 08A0 satnds for: There is no free receive buffer available:No receive buffer space available for receiving data. Corrective action is :The P_RCV FB must be called more frequently. Please use the sample code which you can download fromhere. In this sample code inside FC11 there is a provision for sending two request of different data length from different area of a DB. Already programmed. And if required you can increase it further. Please see below L MB 1 L 2#11 AW DEC 1 JL LIST JU A0 // Requests 1 and 2 JU A1 LIST: JU ENDE A0: L 10 // DB10 T "SEND_DBNR" L 2 // As of DW2 T "SEND_DWNR" L 10 // Length 10 bytes T "SEND_LAE" JU SND A1: L 10 // DB10 T "SEND_DBNR" L 14 // As of DW14 T "SEND_DWNR" L 100 // Length 100 bytes T "SEND_LAE" JU SND // Here you can insert any other requests SND: CALL "P_SEND" , "DB_P_SEND" REQ :="REQ_SP" // Startup R :="RESET_SP" // Execute RESET LADDR :="BGADR" // Logical base address DB_NO :="SEND_DBNR" // MW40 DBB_NO:="SEND_DWNR" // MW42 LEN :="SEND_LAE" // MW44 DONE :="SEND_DONE" ERROR :="SEND_ERROR" STATUS:="SEND_STATUS" A BR = "SEND_BIE" ENDE: BE

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5/15/2012 2:25 PM	Rate (1)
Kaulquappe Posts: 3093 Rating: (323)	smiffy So as long as you call the P_RCV call quicker than once per second, you should be fine. What OB are you using the P_RCV call in? Sorry Smiffy, in this case you are wrong. Each P_RCV call transfers 13 Byte from the CP to the CPU (CP340 manual, section 6.1). When the communication partner sends telegrams without gap and the transmission rate is 9600 baud, P_RCV should be called every 13 ms at least. @ Aevat Does the communication partner send one telegram with more than 1024 byte or does it send several telegrams which sum length exeeds 1024 byte? Does the telegramhave an end character? Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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5/15/2012 2:28 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Aevat How can I program this such that I can be able to receive all the 1034 bytes?... Hello Aevat, CP340 is not capable to receive telegrams with a bigger length than 1024 byte. Would it be possible to split the data to two telegrams? Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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5/15/2012 3:22 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	Kaulquappe Sorry Smiffy, in this case you are wrong. Each P_RCV call transfers 13 Byte from the CP to the CPU (CP340 manual, section 6.1). When the communication partner sends telegrams without gap and the transmission rate is 9600 baud, P_RCV should be called every 13 ms at least. Ah I see. I missed that bit. Thanks my friend. Could it be the problem that the CP340 can only transfer a maximum 1024 bytes per call? If that is the case, could the first call transfer the data to addresses 0 - 1023, then the next call setup to transfer the remaining data to addresses 1024 onwards? This being done by (pseudo code):- Initialise TotRxBytes to 0 and BytesToReceive to the number of bytes you are wanting to get. IF TotRxBytes < BytesToReceive THEN CALL P_RCV (with DBB_NO = TotRxBytes) IF NDR = TRUE THEN TotRxBytes = TotRxBytes + LEN; END_IF END_IF This would receive data in whatever size packets the CP gets and will store it without overwriting any previous data. I have used this method in the past and it has worked for me. Albeit that my data packets were smaller than 1024 bytes, and I was using a CP341. But in theory it should work, provided that you call it in a fast enough OB.
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5/15/2012 4:31 PM	Rate (0)
Aevat Posts: 17 Rating: (0)	Kaulquappe smiffy So as long as you call the P_RCV call quicker than once per second, you should be fine. What OB are you using the P_RCV call in? Sorry Smiffy, in this case you are wrong. Each P_RCV call transfers 13 Byte from the CP to the CPU (CP340 manual, section 6.1). When the communication partner sends telegrams without gap and the transmission rate is 9600 baud, P_RCV should be called every 13 ms at least. @ Aevat Does the communication partner send one telegram with more than 1024 byte or does it send several telegrams which sum length exeeds 1024 byte? Does the telegramhave an end character? Regards, Kaulquappe Yes, it sends only one telegram with more than 1024 bytes. End characters are CR+LF.
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5/15/2012 4:52 PM	Rate (0)
Aevat Posts: 17 Rating: (0)	Kaulquappe Aevat How can I program this such that I can be able to receive all the 1034 bytes?... Hello Aevat, CP340 is not capable to receive telegrams with a bigger length than 1024 byte. Would it be possible to split the data to two telegrams? Regards, Kaulquappe In my case, the expected telegram to be received cannot be splt, which means when the request is made, a data of more than 1024 bytes has to be fetched.
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5/15/2012 5:21 PM	Rate (0)
Marciano Bronze Member Joined: 4/30/2007 Last visit: 3/9/2023 Posts: 231 Rating: (23)	Hello Aevat, check how is you cpu scan time, taking from the posts here it will be desired be less than 13ms. A feasible solution however for you would be decrease the transmission baud-rate.

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